three colorimetric methods for evaluating chloride...

Abstract—The purpose of this study was to evaluate the chloride

penetration depth of cracked and coated concrete by using three

colorimetric methods; including silver nitrate, combination of silver

nitrate and potassium chromate, and combination of silver nitrate

and fluorescein. Three groups of specimens were classified;

including non-cracked, 0.2 mm-cracked, and 0.5 mm-cracked

specimens. Each group was applied with three different types of

surface protection; namely hydrophobic, sealing, and coating

materials. The chloride penetration was accelerated into the

specimens by applying the direct current of 60 voltage for 6 hours.

Thereafter, the specimens were split into halves across their

diameter along the crack plane. The split specimens were then

sprayed with the colorimetric solutions. The results found that

hydrophobic materials exhibited the lowest chloride penetration

depth of non-cracked specimens. Moreover, the coating materials

exhibited good resistance to chloride penetration for cracked and

non-cracked specimens. The silver nitrate and potassium chromate

method was found to observe color change at the chloride-

contaminated zone of the specimens clearly, comparing to the other

methods. Moreover, the depths of chloride penetration measured by

spraying with both the silver nitrate and potassium chromate

solution were no significantly different from those applying with

only silver nitrate solution. Spraying with both silver nitrate and

fluorescein solution was found to be the most sensitive method for

the determination of chloride content at a low concentration.

Keywords— Colorimetric methods, Surface protection, Cracked

concrete, Chloride penetration depth

I. INTRODUCTION

HE acid-soluble chloride content of drilled samples is

commonly used for the determination of chloride content

in the concrete. However, the preparation for testing of the

method is time-consuming, and the method requires to use

expensive equipments and consumable substances.

Alternatively, some researchers [1-6] recommended to use the

Panthawit Watanasrisin is with the Department of Civil and Environmental

Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom,

73170, Thailand (corresponding author’s phone:+668-30678531; e-mail:

[email protected])

Khomkrit Supatnantakul is with the Department of Civil and Environmental


73170, Thailand (e-mail: [email protected])

Thatchavee Leelawat is with the Department of Civil and Environmental


73170, Thailand (e-mail: [email protected])

easier and quicker method for determination of the chloride

penetration depth by using colorimetric method.

Otsuki et al. [3] investigated the different types and

quantities of colorimetric solutions, which included silver

nitrate, lead nitrate, and thallium nitrate solutions. Spraying

with the silver nitrate (AgNO3) solution was observed to

distinguish the clearest color change between chloride-

contaminated zone and free-chloride zone. Otsuki et al [3]

and Myung-Yu et al [4] recommended to dilute silver nitrate

in water with the concentration of 0.1 mol/liter for clearest

color change. Ve´ ronique et al [5, 6] found that spraying

with both silver nitrate and potassium chromate (AgNO3 +

K2CrO4) solutions on the broken surface of concrete was

found to distinguish the color change between chloride-

contaminated zone and free chloride zone easier than

spraying with silver nitrate only. He et al [2] reported that

measurement of chloride penetration depth using spraying

both silver nitrate and fluorescein (AgNO3 + fluorescein)

solutions was found to be deeper than the others.

The surface treatment is commonly used to improve the

performance and the service life of repaired concrete [7-9].

However, very limited researches were found to study the

determination of chloride penetration depth for cracked and

coated concrete using colorimetric methods. Therefore, the

main aim of the study was to investigate the color change of

chloride-contaminated zone for cracked concrete being coated

with various material using the colorimetric methods.

II. METHODOLOGY

A. Materials

Ordinary Portland cement conforming to ASTM C150 [10]

was used in this study. The coarse aggregate was crushed

limestone with the maximum nominal size of 19 mm, and the

fine aggregate was river sand with the maximum nominal

size of 4.75 mm.

Six different surface protection materials, which were

classified into three groups; including hydrophobic, sealing,

and coating materials, were applied in this study. The

hydrophobic materials; including silane (SL) and siloxane

(SX), were used. The sealing material was silicate-based

material (SB). The coating materials; including three

different brands of acrylic coating materials (AA, AB, AC),

were used.

Three Colorimetric Methods for Evaluating

Chloride Penetration of Cracked and Coated

Concrete

Panthawit Watanasrisin, Khomkrit Supatnantakul, and Thatchavee Leelawat

T

International Conference on Chemical, Civil and Environmental Engineering (CCEE’2014) Nov 18-19, 2014 Singapore

http://dx.doi.org/10.15242/IICBE.C1114029 26

The colorimetric solutions used in the study were prepared

from the analytical grades of chemical substance. The silver

nitrate (AgNO3) solution was prepared by diluting the silver

nitrate powder with the de-ionized water to obtain aqueous

solution with the concentration of 0.1 M. Whereas the 5% by

weight of potassium chromate (K2CrO4) solution was

prepared by diluting potassium chromate in 1 liter of the de-

ionized water. Additionally, 1 g/liter of fluorescein

(C20H12O6) solution was prepared by diluting fluorescein in 1

liter of 70% ethyl alcohol.

B. Concrete Proportioning and Specimen Preparation

Concrete mixture was designed for 28-day compressive

strength of 35 MPa. The details of mix proportion are given

in Table I. The concrete mixture was cast in thirty-five ø100

× 200 mm cylindrical moulds. The mixture was poured in

three layers and each layer was consolidated on a vibrating

table for 15 seconds. After casting, the specimens were

covered with plastic sheet for 20±4 hours, demoulded, and

then cured in moist-cured room for 7 days. Thereafter,

seventy ø100×100 mm cylindrical specimens were prepared

by cutting at the middle of thirty-five ø100×200 mm

cylindrical specimens. All of the cut specimens were then

returned to the moist-cured room. At the age of 14 days, the

cut specimens were removed from the moist-cured room and

pre-cracked using a controlled splitting test. Similar

technique used for developing cracks along the surface of

specimens was recommended by Yi et al [11]. Thereafter,

seven points along the crack plane of cut specimens were

measured by a digital microscope and then averaged. The

cracked specimens were separated into two ranges of crack

widths; including 0.1-0.3 mm and 0.4-0.6 mm.

TABLE I

MIX PROPORTIONS

Mix Proportion (kg/m3) w/c

Cement Water Coarse aggregate Fine aggregate

342 205 897 870 0.60

The specimens were then separated into 4 groups based on

the types of surface protection; including uncoated specimens

(non), specimens applied with hydrophobic materials (SL and

SX), specimens applied with sealing material (SB), and

specimens applied with acrylic coating materials (AA, AB,

and AC). Preparation for applying each surface protection

used on the surfaces of specimens was performed according to

the manufacturers’ recommendation.

The uncoated specimens, which were the first group, were

kept in the moist-cured room until the testing age of 28 days.

The cut specimens in the second group were removed from

the moist-cured room at the age of 21 days, cleaned, and

dried in the laboratory condition for 2 days. Thereafter, two

layers of silane (SL) or siloxane (SX) were applied on the

surface of cut specimens. The specimens were then kept in

the laboratory condition until the testing age at 28 days.

The cut specimens in the third group were removed from

the moist-cured room at the age of 14 days. The surfaces of

specimens were roughed using sandpaper and then cleaned.

The silicate-based material (SB) proportioning with the ratio

of 3 parts of powder to 1 part of water was applied on the

surfaces of specimens which were controlled to have the

thickness of coating about 2 mm. The applied specimens

were then allowed to dry in the laboratory condition for 24

hours and transferred to the moist-cured room until the

testing ages of 28 days.

The cut specimens in the fourth group were removed from

the moist-cured room at the age of 21 days, cleaned, and

dried in the laboratory condition for 2 days. Thereafter, one

layer of the acrylic coating material (AA) or the acrylic

coating material (AB) was applied on the surface of cut

specimens. Whereas two layers of the acrylic coating

material (AC) were applied on the surface of the other

specimens. The first layer was proportioned with the ratio of

1 part of AC material and 1 part of water, and then applied

on the surface of cut specimens. The second layer containing

only AC material was applied consecutively on the first layer

of cut specimens. The specimens were then kept in the

laboratory condition until the testing age at 28 days.

At the age of 28 days, chloride ingress was accelerated into

all of the cut specimens by using the electrical potential

method. Preparation of the method was described in ASTM

C1202 [12]. After applied with the 60 Vdc for 6 hours, the

specimens were split across their diameters along the crack

plane and then sprayed with colorimetric solution.

C. Testing Method

Three types of colorimetric solutions; namely AgNO3,

AgNO3 + K2CrO4, and AgNO3 + fluorescein, were used to

evaluate the depth of chloride penetration for coated and

cracked specimens.

The AgNO3 solution was sprayed immediately on freshly

broken surfaces of sixty-three specimens; including non-

cracked and uncoated, cracked and uncoated, non-cracked

and coated, and cracked and coated specimens, and left for 45

minutes. The color changes appearing on the sprayed

surfaces were monitored and the depth of color change for

each specimen was measured from the coated surfaces.

For AgNO3 + K2CrO4 method, the AgNO3 solution was

also sprayed on the freshly broken surfaces of sixty-three

specimens. Next, the broken surfaces were left for 45 minutes

and then sprayed with the K2CrO4 solution, as recommended

by Ve´ ronique et al [5]. The sprayed surfaces were left for

further 10 minutes. The color changes at the sprayed surfaces

were also monitored and their depths of color changes were

measured.

For AgNO3 + fluorescein method, the fluorescein solution

was sprayed on the freshly broken surfaces of the other sixty-

three specimens and left for 3 minutes. Thereafter, the

AgNO3 solution was sprayed on the surfaces of specimens

being sprayed with the fluorescein solution, as recommended

by He et al [2]. The specimens were left for further 3

minutes.



The sprayed surfaces of specimens were photographed.

The contrast of color changes at the sprayed surfaces was then

increased by a graphic program. Thereafter, the depths of

color changes for the sprayed specimens were measured.

III. RESULTS AND DISCUSSION

A. Visual Appearance of Three Colorimetric Methods

Fig. 1 shows the appearance of color change at the split

surfaces obtained from three colorimetric methods.

For the AgNO3 method, the color of chloride-contaminated

zone was change to white or light grey color and the color of

free-chloride zone changed to light brown color as shown in

Fig. 1 (a). The color change was in line with Otsuki et al and

Myung-Yu et al [3, 4], which also found that duration of

changing color depended on reaction between chloride and

AgNO3 on the sprayed surface. In our study, the changing

color of some specimens could be seen in the first 10 to 15

minutes. Noted that, if the specimen was carbonated, the

carbonated area had been changed to white color within 10

minutes after being sprayed. The color change of the AgNO3+K2CrO4 method is shown

in Fig. 1 (b). After being sprayed with the K2CrO4 solution,

the chloride-contaminated zone changed from light grey to

dark grey color and the free-chloride zone changed to dark

brown color. The color changes obtained from the

AgNO3+K2CrO4 method were clearer than those obtained

from the AgNO3 method. It was also found that the

carbonation zone changed from white to red brick color. The

color changes of chloride-contaminated and free-chloride

zones were similar with those reported by He et al.[2] and Ve´

ronique et al [5, 6] and the color change of carbonation zone

was in line with Ve´ ronique et al. [5].

For the AgNO3 + fluorescein method, the color of chloride-

contaminated zone changed to faded pink and color in free-

chloride zone turned to yellow brown as shown in Fig. 1 (c).

The AgNO3 + fluorescein method was found to be the most

complicated method because color change was difficult to

observe clearly. Therefore, image editor software was used to

increase the contrast of color change before measuring the

chloride penetration depth. In this method, no carbonation

zone could be observed.

Fig. 2 shows the color changes of cracked concrete applied

with different types of surface protection. It was found that

hydrophobic materials exhibited red brick frontline inside the

concrete as shown in Fig. 2 (a). It may indicate the chloride

ion penetrating up to this frontline. In addition, small

hydrophobic bubbles could be observed between the coated

surface and the frontline after the colorimetric solution was

sprayed on the broken surface of concrete. This indicated that

hydrophobic materials only adsorbed on the crack walls

without filling all of the crack areas. Therefore, the chloride

ion could be observed to penetrate deeply inside the concrete.

a).AgNO3 method b).AgNO3+K2CrO4 method c).AgNO3 + Fluorescein method

Fig. 1 Color changes obtained from colorimetric methods used

a).Hydrophobic material in cracked

concrete

b).Sealing material in cracked concrete c).Coating material in cracked

concrete

Fig. 2 Color changes of coated specimens having the range of crack width between 0.1 and 0.3 mm

Hydrophobic Sealing Coating



For sealing material, crystallization appearing as white

areas could be observed to fill in the crack areas as shown in

Fig. 2 (b).

Fig. 2 (c) shows that only AC acrylic coating could

penetrate into the cracks, fill in the crack areas, and cover the

upper surface of concrete. The penetration of AC material

assisted in improving the crack-bridging areas. The

penetration depth of AC material was about 20-25 mm from

the applied surface of concrete, depending on the crack

widths and their patterns. However, the other acrylic

materials; namely AA and AB, were found to cover only the

coated surface of concrete without penetrating into the cracks.

In the case of non-cracked specimens, the hydrophobic and

sealing materials were found to penetrate slightly into the

concrete. No penetration depth of coated material was

observed, irrespectively to the brands of coated materials.

B. Chloride Penetration Depth

The chloride penetration depths of three colorimetric

methods are shown in Fig. 3. Non-cracked specimens applied

with surface protection obtained from silane (SL), siloxane

(SX), or acrylic (AC) exhibited the lowest chloride

penetration depth. Since silane (SL) and siloxane (SX) had

very small particle size which could easily penetrate into the

pore of concrete, thereby decreasing the chloride ingress into

the concrete.

In the case of cracked specimens, the acrylic coating

materials exhibited chloride penetration depth, measured by

AgNO3 and AgNO3+K2CrO4 methods, lower than the other

protective materials used. Moreover, acrylic coating (AC)

was found to exhibit the lowest chloride penetration depth,

irrespectively to the measured colorimetric methods. This is

due to the filling cracks, which could be observed only from

acrylic coating (AC) as shown in Fig. 2(c). However, all of

the protective materials used in the study had no significant

difference in chloride penetration depth of concrete

containing with the range of crack width between 0.1 and 0.3

mm, when their depths were measured by AgNO3 +

fluorescein method. Since the AgNO3 + fluorescein method

was sensitive to low chloride concentration as mentioned in

He et al [2]. It could be noted that applying with silane (SL)

or siloxane (SX) on the surface of concrete containing large

sizes of cracks was not an effective method to minimize the

chloride ingress. Since the silane (SL) or siloxane (SX) only

adsorbed on the surface of crack walls without filling the

whole crack areas. Moreover, the chloride penetration depth

of concrete coated with silicate-based material (SB) was

similar to that of the corresponding concrete applying with

silane (SL) or siloxane (SX). Since the silicate-based

material could also penetrate into the pore structures and

cracks inside the concrete (Fig. 2 (b)) and then develop the

crystallization of silicate products in the concrete.

C. Comparison of Three Colorimetric Methods

Fig. 4 shows trend lines obtained from average chloride

penetration depths of three colorimetric methods for all

surface protection materials for each range of crack width

using SPSS program. The chloride penetration depths

increased with increasing the crack width, irrespectively to

colorimetric methods.

Spraying with both AgNO3+K2CrO4 solutions exhibited the

chloride penetration depth slightly higher than spraying with

only AgNO3 solution. The result was in line with Ve´

ronique [5, 6]. Moreover, spraying with AgNO3 + fluorescein

a).AgNO3 method

b).AgNO3+K2CrO4 method

c).AgNO3 + fluorescein method

Fig. 3 Comparison of chloride penetration depth among

surface protection materials used



solution exhibited the chloride penetration depths

approximately 1.5 times higher than spraying with AgNO3

and spraying with both AgNO3 + K2CrO4 solutions. The

finding was in line with He et al. [2]. The AgNO3 +

fluorescein method was the most sensitive method to

determine the low chloride content. However, no significant

difference in the chloride penetration depth obtained from

AgNO3 and AgNO3 + K2CrO4 methods could be observed as

shown in Fig. 5, with a two-side p-value higher than 0.05.

IV. CONCLUSIONS

The hydrophobic and coating materials provided the

better performance against the chloride ingress for non-

cracked concrete.

Only coating materials showed the better chloride

penetration than the other protection materials used.

Coating material AC can penetrate into the crack and

increase the crack bridging ability.

The chloride penetration depths obtained from of AgNO3

solution was no significantly different, when compared to

those obtained from AgNO3 + K2CrO4 method. The

AgNO3 + fluorescein has shown the of chloride

penetration deeper than the other methods.

The AgNO3 + K2CrO4 method provided the clearest color

change among three colorimetric methods. AgNO3 +

fluorescein method exhibited the most unclear color

change. Therefore, the graphic program should be used

to increase the contrast of color change prior to

determination of chloride penetration depth.

ACKNOWLEDGMENT

This study is partially supported by Graduate Studies of

Mahidol University Alumni Association.

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Fig. 4 Chloride penetration depth of three colorimetric method

Fig. 5 Chloride penetration depth between AgNO3 and AgNO3

+ K2CrO4 method



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